Search

Contains fulltext : 291656.pdf (Publisher’s version ) (Open Access)

Following the cessation of dewatering in the southern part of the Durham Coalfield in 1974, groundwater levels rose in both the mine workings and the overlying Magnesian Limestone Aquifer (MLA). A pollution plume has since been migrating through the MLA, with sulphate concentrations greatly exceeding potable water standards. Prediction of future plume development requires specification of whether upflow of mine water to the MLA occurs from a small number of point sources or in a diffuse manner (i.e. distributed over most of the area in which the MLA is underlain by mineworkings). A programme of conceptual and numerical modelling has addressed this issue. Mine plans and geological information were used to characterize the flooded mine system and its interface with the MLA. Piezometric and meteorological data were used to constrain finite difference simulations of groundwater flow in the MLA. Flow velocity vectors derived from these flow simulations allowed modelling of plume migration by solution of the advection–dispersion equation. The results of these simulations illustrate that it is necessary to invoke both point and diffuse upflow to explain the observed patterns of pollutant migration to 2003. Predictive modelling of further plume migration indicates that sulphate concentrations are likely to rise to unacceptable levels in the most proximal public supply wells within the next two decades.

Soil contaminated with explosives was supplemented with carbon-14 labelled 2,4,6-trinitrotoluene ([sup 14]C-TNT) and was composted in a field static pile composting experiment. After 90 d of composting, the distribution of carbon-14 ([sup 14]C) activity in fractions from acetonitrile extraction ([open quotes]free[close quotes] fraction, 1.2% of the initial [sup 14]C-activity) and filtration ([open quotes]insoluble-particle[close quotes] fraction, 17.9%), alkaline hydrolysis ([open quotes]insoluble-hydrolyzable[close quotes] fraction, 56.8%), and combustion of the residue ([open quotes]insoluble-nonhydrolyzable[close quotes] fraction, 4.7%) showed that the bulk of the [sup 14]C-activity, and presumably transformed product(s) of the [sup 14]C-TNT, accumulated in a nonextractable, but hydrolyzable fraction. Repetitive aqueous leaching of the compost and also ultraviolet light irradiation followed by leaching suggest that the insoluble fraction of transformed TNT should not be released appreciably by the action of acid rain or sunlight. 16 refs., 11 figs., 2 tabs.

The interaction of water vapor with freshly prepared bulk YBa2Cu3Oy produces an increase in the number of EPR active Cu2+ ions. For many of the samples studied, the number increased by a factor of about 5. On further exposure to water vapor, the number decreases to approximately its initial value. We suggest that the increase and decrease of the Cu2+ signal is due primarily to residual BaCuO2. The changes in the EPR spectra of BaCuO2 when exposed to water vapor are similar to those observed for YBa2Cu3Oy. These changes occur during the initial stage (first few hours) of exposure to 100% water vapor in air. A different Cu2+ signal is observed from samples soaked in water, probably from the production of Y2BaCuO5.

In cases of strong coupling of electrons or holes to the crystal lattice, a carrier may be self-trapped as a small polaron in its own lattice distortion field. A bound electron-hole pair involving such a carrier is generally described as a self-trapped exciton, and it may dramatically influence luminescence, energy transport, and lattice defect formation in the crystal. The phenomenon of exciton self-trapping is particularly common in metal halide and rare-gas crystals, where the strong exciton-lattice coupling can usually be ascribed to the possibility of covalent bond formation in the excited state of a crystal which does not admit such bonding in its ground state. Alkali halides are the most thoroughly studied of these materials. This paper will review experimental data, primarily spectroscopic, and theoretical treatments, primarily by methods developed for defects in solids, on the nature and consequences of self-trapped excitons.

Previously, a so-called excess degrees-of-freedom problem associated with sidelobe cancellers whose adaptive weights are selected using conventional least squares min- imization methods was identified. This problem is man- ifested by rising sidelobe levels and falling output signal- to-interference-plus-noise ratios as the number of degrees of freedom surpasses the number of interferers. In this paper we describe how principal components analysis methods can be used to resolve the ill effects of processing with excess degrees of freedom. Simulation results are presented which compare the performance of conventional least -squ ares and principal components based techniques.

The authors discuss a 3 km diameter sparse planar antenna array facility for wide-bandwidth (1 MHz) high-resolution (1 degrees ) spatial processing experimentation for high-frequency (4-30 MHz) sensor and communication systems. It is demonstrated that both interference and noise can be canceled across a 1-MHz band using adaptive array processing methods. It is found that, while the HF environment is essentially stable over short time intervals (64 ms), significant variations may occur over longer periods (1 min), and these variations may significantly impact the performance of conventional beamformers and constrained least-squares adaptive array algorithms. Robust techniques, including diagonal loading and a signal subspace projection based approach, were successfully applied to reduce the sensitivity of the adaptive array to both calibration errors and fluctuations in the HF channel. Adaptive sidelobe cancellation techniques were combined with matched filtering to detect spread-spectrum signals. >

The performance of high frequency (HF) radio communication and radar systems can be limited by noise generated by sources external to the receiving antenna. Below 10 MHz, atmospheric noise generated by worldwide thunderstorm activity tends to be the dominant natural source. We present an empirical analysis of atmospheric noise cancellation achieved by applying an adaptive sidelobe canceller to wideband HF signals measured using the MITRE Texas Facility. We couple our empirical analysis with predicted results obtained using CCIR noise models to assess the likelihood of obtaining significant levels of noise cancellation. We also describe cancellation performance as a function of the degrees of freedom applied and variations in data block size. >

The authors present an analysis of the performance of a concurrent blocked sidelobe canceler when there are more auxiliary array elements, or degrees of freedom, than spatially coherent interferers. The existence of an excess degrees-of-freedom problem for the concurrent processor is reconsidered. The main result is the analytic determination of tight bounds for the mean square error for the concurrent blocked sidelobe canceller in the excess-degrees-of-freedom region. The performance of a sidelobe canceller applied to a 1000 element planar array having a circular aperture with a radius of 100 wavelengths is shown. >

The authors describe an experimental analysis of adaptive array processing techniques conducted using a 16-element high frequency (HF) array. The results demonstrate the ability of these techniques to cancel both narrow-bandwidth interference and wide-bandwidth noise. The effects of calibration errors and the nonstationary HF channel on beamforming and constrained adaptive processing are discussed. The HF channel will support both beamforming and constrained processing over short time intervals. However, for longer periods robust adaptive array processing techniques may be required. Two robust methods are described, the diagonal loading algorithm and a principal components projection method. It is shown that adaptive array processing algorithms can be used in conjunction with a matched filter to extract a spread-spectrum signal from interference. >

The topographical changes in the asperities of a flat cobalt-hardened gold electroplated surface that occur as a result of being contacted by a sphere are simulated by computer superposition of a mathematically generated spherical surface and a Scanning Tunneling Microscope topograph of an actual flat sample surface. Both ideally smooth and rough spherical surfaces are considered. Two-dimensional maps of the location and size of contact areas and quantitative information on contact areas resulting from asperities that would have been deformed in actual contact events are presented. In addition, 3-dimensional plots and quantitative values of the location and volume of asperity material that would have been deformed in actual contact events are presented. Good agreement is found when the simulation results are compared with experimentally obtained contact results for the same sample surface region at the same indention depth. The simulation technique should prove useful in predicting changes in contact performance associated with changes in contact surface topography or contactor geometry. Computer simulation is much faster and easier than obtaining similar information by experimental techniques which are time consuming and require sophisticated sample contact and positioning hardware.

The topographical changes to the asperities of a flat cobalt-hardened gold electroplated surface that occur as a result of being contacted with a ruby sphere are studied by means of scanning tunneling microscopy and software developed to allow computer image registration and subtraction. A range of normal, force loads and sphere sizes are utilized. Quantitative information is obtained for each plastically deformed asperity in the contact region concerning the volume of material displaced during the contact process and the area of the contact spot resulting from the flattened asperity. Three-dimensional images are presented that show the location and size of the portions the asperities that were displaced in the contact process. Two-dimensional maps are generated to show the location and size of the asperity contacting spots in the contact region, Data from contact conditions of 10 to 100 grams normal force and from 1/16 inch to 1/4 inch contacting sphere diameter are used to show trends concerning the number of deformed asperities, total contacting area, total deformed volume, maximum area of the largest deformed asperity, force/total contacting area, and total deformed volume/total contacting area as a function of normal force and sphere diameter.

A method of parameter estimation is presented for a class of problems in which the desired signal is embedded in colored noise with unknown covariance. The proposed algorithm does not require multiple estimates of the signal covariance matrix; instead, it uses a priori knowledge of the structure of the noise covariance matrix to transform the array covariance matrix in a way that leaves its noise component unchanged while the signal component is transformed in some appropriate manner. The noise component is then eliminated by forming the difference of the original and transformed covariance differencing methods to be applied to a wider class of problems than was previously possible. This is illustrated by applying the algorithm to the problems of bearing estimation, resolution of overlapping echos, and transient response analysis. Simulation results demonstrate that the technique affords significant improvement in certain situations over conventional methods. >

Thrust sheet movement over ramps requires energy because of the frictional resistance and deformation within the fault zone, fault-bend folding at the base and top of the ramp, and changes in the gravitational potential energy because of uplift. To model the energy usage, a kinematic model of a foreland thrust sheet is constructed assuming: (1) the ramp is planar and the flats are parallel to bedding; (2) the fault-bend folds are concentric; (3) thickness is preserved for beds that enter the folds parallel to the basal thrust fault and (4) cross-sectional area is preserved for rocks deformed by folding. Equations for the work done within the fault zone, and during uplift and fault-bend folding are derived by combining the kinematic model with stresses that increase in proportion to depth. The relative amounts of energy consumed by friction along the fault, uplift and fault-bend folding are estimated to be 2.7:1.0.25 for a ramp angle of 30°. The energy balance for the movement of large thrust sheets thus depends principally upon friction in the fault zone and changes in the gravitational energy.

A number of adsorbents have been characterized using small-angle neutron scattering (SANS) and the results compared with those obtained by analysis of nitrogen sorption isotherms. The adsorbents include the microporous Gasil 200 and 60 120 mesh silicas, charcoal cloth, and activated charcoal; the mesoporous Gasil 35, Spherisorb S20W, and S7W silicas, the Spherisorb AIOY, Harshaw (support and supported catalysts) aluminas; the nonporous Cabosil and precipitated silicas, Alon alumina, a graphitized and ungraphitized carbon black (Sterling FT), Koch-Light graphite, and two naturally occurring iron pyrite samples (EOD and MT. ISA); a series of electrofurnace graphites A to H having N 2 BET areas in the range 5 to 540 m 2 g −1 . Guinier plots of the small-angle neutron scattering data indicate that the porous materials studied are particularly well defined in terms of their porosity. Linear Guinier behavior suggests that the pores approximate to a monodisperse phase in a binary phase system. With the exception of activated charcoal, the scattering is best approximated by the Guinier “cylinder” relationship. The SANS pore sizes (from Guinier analysis, assuming a cylindrical pore shape) agree reasonably well with those from conventional analysis, e.g., by application of the Kelvin equation to desorption isotherms and porosimetry. This was shown by the Spherisorb silicas (48 to 76 A (SANS), 89 A (other)), Gasil 35 (76 A (SANS), 120 A (other)), Gasil 200 (23 to 39 A (SANS), 21 A (other)), mesh silica (14 A (SANS), 21 A (other)), Spherisorb alumina (101 A (SANS), 134 A (other)), Harshaw support (51 A (SANS), 79 A (other)), Harshaw catalysts (100 A (SANS), 100 A (other)). The SANS technique was also used in the detection of a change in the pore form of a catalytic alumina support. The process used to introduce the copper chloride Harshaw catalyst into the supporting alumina appeared to increase the size in terms of an increased radius. Additionally, the pore shape changes from one which gives rise to scattering according to an isodiametric cylinder. The presence of a monodisperse phase consisting of micropores within charcoal cloth and activated charcoal was confirmed by Guinier analysis. The nonporous solids show universal nonlinear Guinier behavior as a result of the polydisperse nature of the heterogeneities present. Normal Porod behavior, i.e., Q −4 dependence of the scattered intensity, I , at high momentum transfer, Q , was shown by the mesoporous and nonporous silicas and aluminas. Q −2 dependence of I was found for the microporous silicas and charcoal cloth. Q − n dependence of I was found for the other adsorbents where n showed values of 2.7 (activated charcoal), 316 to 2.8 (graphites A to H), 3.9 (Koch-Light graphite, 3.5 to 4.0 (graphitized and ungraphitized Sterling FT, respectively), 3.3 to 3.5 (iron pyrites). The Porod plots can be classified into four types depending on the shape and gradient of the curve; the shape of the Porod plot provides an immediate “visual” indication of the porous nature and dispersivity of the heterogeneities within an adsorbent. The exponential Debye correlation function (exp(− r/a )) fits the results shown by the solids investigated although indicating an essentially random structure. The addition of a small Gaussian correction term (exp(− r 2 / a 2 2 )) was necessary for most adsorbents. SANS specific surface areas have been determined for all the adsorbents by the following techniques (where possible): 1. (i) Using the corrected asymptotic value of IQ 4 (as Q → 0) from modified Porod plots, with I measured in absolute units of intensity. 2. (ii) Using the Debye parameters a and A , to yield a corrected value of IQ 4 , i.e., A/a 4 , in absolute units of intensity. 3. (iii) Using void fractions and the Debye parameter a , (from nonabsolute intensity measurements). Good agreement was found between the SANS areas by method (i) and BET surface areas for solids with BET areas less than 11 m 2 g −1 , namely iron pyrites, graphite A, Koch-Light graphite, Sterling FT. Poor agreement was found between the SANS and BET areas for the microporous adsorbents and graphites B to H. The SANS areas of the microporous adsorbents were less than 100 m 2 g −1 compared with BET areas in the range 650 to 1500 m 2 g −1 . The trend showing an increase in the BET area of 24 m 2 g −1 (graphite B) to 540 m 2 g −1 (graphite H) was not clearly reflected in the corresponding SANS areas of 6 m 2 g −1 (graphite B), 24 ± 8 m 2 g −1 (graphites C, D, E, F, and G), 60 ± 16 m 2 g −1 (graphite H). The SANS areas of the nonporous and mesoporous aluminas and silicas were of the correct order of magnitude compared with the BET areas. The SANS area of Alon (101 m 2 g −1 (SANS), 87 m 2 g −1 (BET)) and of A1OY (126 m 2 g −1 (SANS), 92 m 2 g −1 (BET)) was greater than the corresponding BET area. The converse was found for the other mesoporous and nonporous silicas and aluminas; the SANS (i) areas were about 50 to 100 m 2 g −1 less than the corresponding BET areas. SANS areas by method (ii) were found to agree reasonably well with the BET area except for activated charcoal (5000 m 2 g −1 (SANS), 650 m 2 g −1 (BET)), ungraphitized Sterling FT (300 m 2 g −1 (SANS), 9 m 2 g −1 (BET)), iron pyrites −MT. ISA (27 m 2 g −1 (SANS), 2 m 2 g −1 (BET)) and EOD (277 m 2 g −1 (SANS), 2 m 2 g −1 (BET)). Good agreement was found between the SANS areas by method (iii) and the BET areas for the mesoporous silicas and A1OY. The SANS areas of the microporous silicas (∼ 1200 m 2 g −1 ), charcoal cloth (2000 m 2 g −1 ), and Harshaw catalysts (280 m 2 g −1 ) were greater than the BET areas (830, 1500, 90 m 2 g −1 , respectively. The SANS area of the Harshaw alumina support, 97 m 2 g −1 , was less than the BET area of 205 m 2 g −1 .

Charcoal cloth has been characterized by small angle neutron scattering (SANS) and sorption techniques. A SANS gyration radius of 10Awas obtained for the charcoal cloth compared with a gyration radius in the range 6 to 9Afrom the Dubinin—Rudushkevich (DR) nitrogen and benzene “ B ” values. The charcoal cloth pores approximated a cylinder shape in the SANS analysis. Type I sorption isotherms of benzene (303 K) and nitrogen (77 K) on charcoal cloth confirm its predominantly microporous nature with a surface area in excess of 1000 m 2 g −1 , and obeyance of the Gurvitsch rule giving a pore volume of 0.65 cm 3 g −1 . A type V water (303 K) isotherm showing linear Dubinin behavior in the range 0.3 0 −1 is smaller than the N 2 BET monolayer capacity (14 mmole g −1 ).

It is well known that signal subspace algorithms perform poorly when coherent or highly correlated signals are present. Recently, the so-called spatial smoothing technique was devised to preprocess the array covariance matrix so that signal subspace algorithms can be applied irrespective of the signal correlation. Unfortunately, the application of this technique reduces the effective aperture of the array. A modified spatial smoothing technique that is capable of increasing the effective aperture of the array over that of conventional spatial smoothing methods is explored. It is shown that under certain conditions, the modified algorithm may fail to yield the desired increase in array aperture, and some simulation results concerning the sensitivity of the modified spatial smoothing algorithm to these conditions are provided. >

Luminescence from TIBr single crystals at low temperature has been investigated using continuous X-ray and UV excitation as well as pulsed-electron-beam excitation. Four emission bands were observed consistently at 495, 504, 560 and 650 nm, with relative intensities dependent on sample preparation, mode of excitation and measurement temperature. The 560 nm band is shown to be associated with excess thallium at the sample surface. Deformation of the crystal at low temperature (e.g. 9°K) produces recombination centers giving rise to the 504 nm and 650 nm luminescence. Subsequent annealing at temperatures of the order of 120°K causes a decrease in the 504 nm luminescence and the simultaneous appearance of the 495 nm band. These observations are interpreted in terms of the thermal release of recombination centers from the vicinities of the dislocations where they are generated.

A new beam line for X-ray lithography with photon energies near 100 eV has been installed on the SURF-II storage ring at the National Bureau of Standards. Vacuum isolation of the ring from the exposure chamber is achieved using both a thin carbon window and a baffle cooled to liquid nitrogen temperature. The design and performance of the beam line are described. Initial exposures of two photoresists of intermediate sensitivity show that the beam line will serve for production of test microcircuits.

4-Nitrophenylarsonic acid is a strong acid, pKa 3·1 and 7·8. When given orally (33 mg/kg) to hens it is slowly excreted, 50% being excreted in 24 hr and 60–80% in 3 days. Complete excretion takes 7–9 days. When given intramuscularly at the same dose, excretion is rapid and 90% is excreted in 24 hr. The only transformation product found in the excreta was arsanilic acid (4-aminophenylarsonic acid) and the amount of this excreted depended upon the route of administration. On oral administration, about 20% of the dose (nearly 30% of the total drug excreted) was excreted as arsanilic acid in 3 days. On intramuscular injection, however, 4-nitrophenylarsonic acid was largely excreted unchanged, only 6% of the dose appearing as arsanilic acid. The reduction of 4-nitrophenylarsonic acid to arsanilic acid was found to take place mainly in the crop and it occurred to a greater extent in well-fed hens than in starving or poorly-fed hens. The enzyme system responsible for the reduction appears to be mainly of microbiological origin. Hen-liver homogenates were also found to be able to carry out this reduction, the activity being associated with the liver microsomes but not with the mitochondria. Studies of the output of 14C (using [1-14C]-4-nitrophenylarsonic acid), total arylarsonic acid and total arsenic suggest that little, if any, inorganic arsenic is released in the hen following the oral administration of 4-nitrophenylarsonic acid. Arsenoxides were not detected in the excreta, but it was found that when 4-nitrophenylarsonic acid was incubated anaerobically with hen faeces it was converted to arsanilic acid, 4-nitrophenylarsenoxide and 4-aminophenylarsenoxide, these compounds being detected chromatographically. Arsanilic acid was also converted into 4-aminophenylarsenoxide under the same conditions. It is suggested that the growth-promoting effect of these arsonic acids may be due to reduction in the gut to the more toxic arsenoxides which may exert a parasitostatic effect in situ in the gut.

A method is presented for the determination of molybdenum by extraction of its thiocyanate complex with methyl isobutyl ketone. The method is accurate to ±4% or 3 μg of molybdenum, whichever is greater. The only elements which cause interference are rhenium (serious), platinum, palladium, rhodium, selenium and tellurium. The method has been applied to a number of standard samples with excellent results.

A method is described for the determination of trace amounts of zirconium and titanium. The two elements are separated from the sample matrix by precipitation with eupferron using iron as a carrier. Zirconium is determined after extraction with TOPO (tri-n-octylphosphine oxide), by colorimetric measurement of the zirconium-Pyrocatechol Violet complex. Titanium is determined by colorimetric measurement of its thiocyanate complex extracted with TOPO. The method is accurate to within ±5% (relative) or ±2.5 ,μg, whichever is greater, for both elements. Using the modifications suggested, the method is nearly specific for the determination of titanium (milligram amounts of niobium cause slightly high results), and only thorium and hafnium interfere with the determination of zirconium.

Experimental correlations are established among steady state optical and ESR spectra and transient luminescence and optical absorption. These correlations support the existence of self-trapped holes in the form of substitutional Ag2+ in AgCl and imply that intrinsic electron-hole recombination is the source of a strong emission band around 2.4 eV.

Dehydroacetic acid (DHA) labeled with C14 in four carbon atoms has been synthesized. DHA administered orally to rabbits at a dose level of 250 mg/kg did not increase the urinary excretion of glucuronides or ethereal sulfates. Small oral doses (20–70 mg/kg) of C14-DHA were not rapidly excreted. In 3–7 days rabbits excreted 70–80% of the dose in the urine, 7–10% in respiratory CO2, and 2–3% in the feces; 8–17% remained in the tissues. In 4–5 days, rats excreted 20–40% in the urine, 10–25% in respiratory CO2, and 10–20% in the feces; 5–26% remained in the tissues. In both rats and rabbits the highest radioactivity was found in the blood. Electrophoresis of human serum incubated with C14-DHA showed that DHA is mainly associated with serum albumin and to a lesser extent with serum globulins. Three metabolites of DHA have been isolated from rabbit urine: triacetic acid lactone (TAL); a hydroxy-DHA, probably 3-glycoloyl-6-methyl-2,3-dihydropyran-2,4-dione; and metabolite X, which is probably the salt of triacetic acid lactone 3-carboxylic acid. A further metabolite, compound Y, which is not a pyrone but probably a degradation product of DHA, was detected. DHA and hydroxy-DHA react with ammonium salts to form the corresponding 1′-imino derivative, imino-DHA and imino-hydroxy-DHA. After administration of DHA to rats and rabbits, the DHA and hydroxy-DHA occur in the urine partly free and partly as the imino derivatives. The urines of rabbits receiving small oral doses of C14-DHA contain an average of DHA (total) 5% of the dose, hydroxy-DHA (total) 20%, TAL 10%, urea 0.3%; metabolites X and Y were estimated to account for 20 and 15%, respectively. Similarly, rat urines contain DHA (total) 5%, hydroxy-DHA (total) 8%, TAL 1%, and urea 0.3%. At higher dose levels the percentages of dose excreted as DHA and hydroxy-DHA are markedly increased, and the percentages as metabolites X and Y markedly decreased. 2,6-Dimethyl-4-pyrone and its 3-carboxylic acid, deoxydehydroacetic acid; orcinol; malonic, succinic, oxalic, and acetic acids; and acetone were shown not to be urinary metabolites of DHA. DHA and hydroxy-DHA, but not TAL, were found in the feces and gut contents of rats after subcutaneous injection of DHA, suggesting that these two compounds are excreted in the bile. The pattern of excretion of metabolites after injection of DHA did not differ significantly from that following oral administration. C14-DHA was metabolized by rat liver, but not kidney, to hydroxy-DHA, TAL, and CO2. A pathway for the metabolism of DHA via hydroxy-DHA, compound X, TAL, and triacetic acid to acetoacetic acid and CO2 is suggested. Because of the reactivity of the keto group of the acetyl side chain and the tendency of DHA and hydroxy-DHA to combine with the amino groups of proteins and other essential compounds, the administration of DHA might have serious deleterious effects. The ultraviolet absorption spectra, color reactions, and chromatographic behavior of the metabolites of DHA and a number of other pyrones are given.

Arsanilic acid (4-aminophenylarsonic acid) is excreted unchanged by hens and there is no evidence that it is converted into any other compound or into inorganic arsenic. It is rather more rapidly excreted after intramuscular injection than after oral dosing, for at a dose level of 50 mg/kg about 64% of the dose is excreted in one day, whilst after injection about 83% is excreted in one day. Arsanilic acid appears to be poorly absorbed. Acetylarsanilic acid (4-acetamidophenylarsonic acid) when given orally in doses of 50 mg/kg is largely excreted unchanged, but a small proportion (5–6%) is deacetylated to arsanilic acid. However, if acetylarsanilic acid is injected intramuscularly into hens it undergoes more extensive deacetylation (36%) which occurs only in the kidney and which is associated with the mitochondrial fraction of kidney homogenates. These findings suggest that acetylarsanilic acid is poorly absorbed in the hen. Both arsanilic and acetylarsanilic acids are strong acids—their pKa's and absorption spectra are recorded.

A strong transient optical absorption band on the exciton shoulder has been observed in pure alkali iodine crystals following pulsed electron irradiation. The ultraviolet transition is ascribed to creation of a second exciton in the vicinity of a self-trapped exciton. The perturbation caused by the proximity of the self-trapped exciton lowers the energy needed to form the second exciton by 0.14 eV for KI and 0.12 eV for RbI.

The Transient Tracers in the Ocean (TTO) study was an experiment to investigate ocean mixing as deduced from the distribution of radiochemical tracers introduced into the atmosphere and subsequently into the oceans during the 1958-1962 nuclear bomb tests. The results of this study together with knowledge about the chemistry of oceanic CO{sub 2} can be used to help understand oceanic uptake of fossil fuel CO{sub 2}. The experiment lasted 4 years and consisted of the following parts: (1) (1981); (3) laboratory analysis (1982); and (4) completion, data analysis, and reporting (1983). Shipboard measurements were published by the Scripps Physical and Chemical Oceanographic Data Facility as the T.T.O. Preliminary Hydrographic Data Reports Vols. I-IV. Recently, revisions to some of the previously reported measurements have been made and estimates of total CO{sub 2} have been calculated.

Color centers in yttrium aluminum garnet have not been as heavily studied as in halides and some other oxides. The studies which have been done were usually undertaken from the perspective of minimizing defects and photo-induced absorption which can degrade the laser performance of Nd:YAG.(1-7) In the hope of developing broadly tunable visible and near-ultraviolet color center lasers in oxide crystal hosts including YAG, we have undertaken efforts to maximize rather than minimize certain defects and to explore their photoluminescence properties. In this paper we address a defect which absorbs at 370 nm and emits in a broad band at 400 nm in undoped (as well as Nd doped) YAG grown under a partial CO reducing atmosphere at the Shanghai Institute of Optics and Fine Mechanics. The photo luminescence was first observed in 1974 by one of the authors (G. Wu)(8) in crystals grown by the method to be described below.

In recent years a new, and very powerful technique for parameter estimation - the eigenstructure, or signal subspace method - has been developed. Eigenstructure algorithms are closely related to Pisarenko's method for estimating the frequencies of sinusoids in white Gaussian noise. In theory they yield asymptotically unbiased estimates of arbitrarily close parameters, independent of the signal-to-noise ratio (SNR). Although signal subspace methods have proven to be powerful tools, they are not without drawbacks. An important weakness of all signal subspace algorithmis their need to know the noise covariance explicitly. The important problem of developing signal subspace based procedures for signals in noise fields with unknown covariance has not been satisfactorily addressed. It is our intent to propose a solution to the problem of direction-of-arrival (DOA) estimation for a broad class of unknown noise fields. We will then briefly discuss other important estimation problems for which modified versions of this procedure can be applied.

Through both theoretical developement and simulation the method we have put forward has been shown to yield improved performance over the conventional spatial smoothing algorithm. Our discussion has demonstrated that for a given array length the proposed method can be used to increase the number of coherent signals that can be resolved and thus effectively increase array aperture. Our simulation results underscore this fact. As we will see this increase in aperture is obtained, to some extent, at the expense of robustness.

4-Hydroxy-3-nitrophenylarsonic acid (“3-Nitro”) is a strong organic acid (pKa, 3·2, 5·8 and 8·9). When administered orally to hens it is relatively slowly excreted. At a dose level of about 19 mg/kg nearly 50% is excreted in 24 hr, at 38 mg/kg 37% and at 75 mg/kg, about 25%. About 9–11 days is required for the complete excretion of a single oral dose of 75 mg/kg. On intramuscular injection the compound was lethal at a dose of 38 mg/kg. However, it was much more rapidly excreted on injection than on oral dosing and of an intramuscular dose of 19 mg/kg, 80% was excreted in 24 hr and over 95% in 3 days. The only transformation product of “3-Nitro” found in the excreta was 3-amino-4-hydroxyphenylarsonic acid and this amounted to 18% of the dose (nearly 25% of the output) in 3 days after an oral dose of 19 mg/kg. On injection, “3-Nitro” was mainly excreted unchanged, the amount of the amino compound excreted being only about 4% of the dose. The extent of reduction depended upon diet, it being lower in starved hens than in well-fed hens. The reduction of “3-Nitro” appeared to take place mainly in the crop and it appeared that this organ also controlled the elimination of the compound when given orally. A comparison of the elimination of the drug with that of polyethylene glycol suggested that it was poorly absorbed in the hen. Analyses of the total arsonic acid and total arsenic excretion indicated that the compound was stable in vivo.